Join Susan as she obsesses about cosmetic chemistry and other things (some possibly related to monkeys). Often strange, occasionally useful, and always worth a stop as a point of interest on your journey through the Intertron.

Sunday, September 27, 2009

A demonstration of HLB

I'm going to take a lotion recipe you've probably seen before (in this post) and use this as a demonstration of how to use the HLB system to create an emulsifying system.

As a note before starting, there are so many ingredients that aren't available to us as homecrafters, so we're kind of stuck when it comes to emulsifiers. I'm going to use glycol distearate and ceteareth-20 as my emulsifiers for this project because that's what I have available to me (from Voyageur and Brambleberry respectively). When you're using your emulsifiers, skin feel is really important as well. Some combinations are unappealing and some combinations won't appeal to you specifically. This is where experimentation is your friend!

This is a pretty basic lotion, so it's a good starting point for our HLB calculations.

WARNING: Math ahead! I know some people aren't fans of math and don't think themselves good at it, but don't be alarmed. If you follow the steps and remember your elementary school math for finding percentages, it's actually quite simple.

There are two phases of HLB math - finding out the HLB value of your ingredients, then finding the HLB value of your chosen emulsifiers.

The steps to finding out the HLB value of your ingredients.

1. Which ingredients have an HLB value?

2. How much of each ingredient is in the total recipe?

3. Multiply this by the total oil phase to get a percentage.

4. Multiply the percentage by the HLB value. Add them together to get the HLB value of your oil phase.

The steps to finding out the HLB value of your emulsifiers.

1. Find a low HLB emulsifier and a high HLB emulsifier.

2. Work on the percentages to find a total that is very close to the HLB value of your oil phase.

3. Rejoice!

STEP 1: Figure out which ingredients have an HLB value.

This is basically your oil phase. Anything that wouldn't go in the water phase probably has an HLB value. Our oil phase (which makes up 23% of our recipe) contains oil, butter, and cetyl alcohol. Each of these has an HLB value.

Olive oil - HLB value: 7

Rice bran oil - HLB value: 7

Shea butter - HLB value: 8

Cetyl alcohol - HLB value: 15.5

STEP 2: Percentage of recipe

How much of each ingredient is in the total recipe? Let's call this number our "recipe %" number.

Olive oil - 7%

Rice bran oil - 8%

Shea butter - 5%

Cetyl alcohol 3%

Total: 23% of the recipe is the oil phase. (Let's call this number our "total oil phase %")

STEP 3: Multiply the amount in the recipe by the total oil phase.

We know our oil phase is equal to 23% of the recipe. So we need to figure out the percentage of each ingredient in the oil phase.

recipe %

total oil phase %

Divide the % in oil phase by the oil phase %.

Olive oil - 30.5% of the oil phase (7 divided by 23) - 0.305

Rice bran - 34.8% of the oil phase (8 divided by 23) - 0.348

Shea butter - 21.7% of the oil phase (5 divided by 23) - 0.217

Cetyl alcohol - 13.0% of the oil phase. (3 divided by 23) - 0.130

This should total 100%. Yep, it checks out.

Note: Remember that a percentage also has a decimal value. For instance, 30.5% is equal to 0.305 (move the decimal two spaces to the right to get the percentage!) These are the values you want to work with in the rest of the phases.

STEP 4: Multiply the numbers from step 3 by the HLB value.

Olive oil makes up 30.5% of the oil phase. It has an HLB value of 7. 0.305 x 7 = 2.135

Rice bran oil makes up 34.8% of the oil phase. It has an HLB value of 7. 0.348 x 7 = 2.436

Shea butter makes up 21.7% of the oil phase. It has an HLB value of 8. 0.217 x 8 = 1.736

Cetyl alcohol makes up 13.0% of the oil phase. It has an HLB value of 15.5. 0.130 x 15.5 = 2.015

Add these numbers together and you get 8.322 (or 8.3) as the HLB of your oil phase.

CHOOSE YOUR EMULSIFIER

To make a good emulsifying system I need a low HLB emulsifier and a high HLB emulsifier working together. I have chosen glycol distearate (also known as EZ Pearl) with an HLB value of 1 and ceteareth-20 with an HLB value of 15.2. (This is a standard combination for emulsifiers and feels very nice). I'm going to use 4% as my starting number for amount of emulsifier because we want to make sure we have enough emulsifier! (I know LabRat recommended 2%, but he was a gifted cosmetic chemist who had years of experience under his belt! If you want to go with 2%, that's just fine, but I want to make sure there's enough emulsifier for this lotion!)

We could have chosen a number of different combinations; I've chosen this one as LabRat posted regularly about this being a good combination and because these are ingredients easily available to the home crafter.

Now we need to figure out how to combine these.

If we use 50% glycol distearate (1) and 50% ceteareth-20 (15.2) we're going to get an HLB of 8.1.

The math...

Glycol distearate: 0.50 x 1 = 0.5

Ceteareth-20: 0.5 x 15.2 = 7.6

HLB for this emulsification system: 8.1

Although we could get closer to our HLB of 8.322 by mixing 48% glycol distearate (0.48) and 52% ceteareth-20 (7.904) for a total of 8.38, this is going to be a huge pain in the bum. We're working with 4%, so you'd have to have 2.1% ceteareth-20 and 1.9% glycol distearate. It's easier to just do 50-50 right now. Given most of the HLB value of emulsifiers are listed as + or - 1, our ceteareth-20 could have a value of 14.2 to 16.2, so we're not being foolish by using 0.1 less of one emulsifier and 0.1 more of another.)

So we have determined that a 50/50 mix of glycol distearate and ceteareth-20 will make up an HLB value suitable for our emulsifier. We're going to start at 4%, which means we'll be using 2% glycol distearate and 2% ceteareth-20 in this lotion.

We multiply the amount of ceteareth-20 we'll need by 4% (our starting point) to figure out how much to use. Put your percentages into decimals - 50% ceteareth-20 is 0.50 and 4% of the emulsifier is 0.04.

0.50 ceteareth-20 x 0.04 = 0.02 or 2% ceteareth-20.

0.50 glycol stearate x 0.04 = 0.02 or 2% glycol distearate

Yeah, I know this one is easy - just divide 4% in half to get 2%. But they aren't always this easy. I fluked out here!

There's the recipe. Want to get more complicated? Try this with your favourite lotion recipe.

And yes, I should be including the fragrance and/or essential oil in the oil phase with an HLB value but I didn't because I really didn't feel like looking up those HLB values! I think I've done enough work today!

Join me for more fun with the HLB system in a lotion with a more complicated oil phase.

Hi Bajan Lilly! With the HLB system, there isn't a hard and fast rule about how much emulsifier to use. Some people like to start at 2% emulsifier and work up from there. I find 4% tends to create a good emulsification system, but you could use 10% if you wanted. It's really up to you how much you want to use, but I tend to use 4% to 5% depending upon the oil phase.

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Who the heck is Swift?

I'm an aspiring cosmetic scientician and DIY girl interested in pretty much any craft you can name - bookbinding, jewellery making, sewing, paper crafts, polymer clay - but my main passion is bath & body product making.
I am currently obsessed with Rock Band (bass and singing) and science books. Did you know my favourite word is "toaster" and my favourite adjective is "hirsute"?